MATERIAL RESPONSE OF A SEMICRYSTALLINE THERMOPLASTIC POLYMER AND COMPOSITE IN RELATION TO PROCESS COOLING HISTORY

A model capable of predicting the process-induced macroscopic in-plane material response of semicrystalline thermoplastic matrices and their composites was developed. This investigation focused on the material response of a single layer or ply of neat PEEK matrix and its carbon fiber composite (APC-2) when subjected to various processing histories. Specifically, the response of the material moduli and processing strains as a function of temperature and the degree of crystallinity were studied. The kinetic-viscoelastic response of the matrix was determined from a modified form of the Standard Linear Solid model. A constitutive relation was proposed to quantify resin shrinkage as a function of thermal history, which incorporated crystallization. For a specific process history, the effective composite mechanical properties were determined from micromechanics models. Both neat and composite processing strains were evaluated to show the effect of fibers on the matrix dominated response (90-degrees direction). In addition, comparisons of model moduli predictions with experimental measurements were performed. This study demonstrated that an increase in the degree of crystallinity results in an asymmetric shift of the modulus in the glass transition region to higher temperatures. Also, strains due to crystallization were predicted to be much smaller in comparison to the strains resulting from thermal contraction of the PEEK matrix.